Two CArG box domains at -140 and -100 bp in the human alpha-cardiac actin gene promoter act synergistically and mutually dependently as tissue-specific regulatory upstream elements for transcription.
An upstream region from the transcription initiation site to -177 base pairs (bp) of the human alpha-cardiac actin gene directs the transient expression of a bacterial chloramphenicol acetyltransferase (CAT) gene only in muscle cells (A. Minty and L. Kedes, Mol. Cell. Biol. 6:2125-2136, 1986). We modified this promoter region by additional 5' deletions, linker-scanning mutations, and insertion-deletion mutations and demonstrated that the asymmetrical sequences in and adjacent to two CArG for CC(A + T rich)6GG motifs, located at -140 and -100 bp, play an important positive role in transcription. The significant impairment of transcriptional activity that accompanies the disruption of one CArG box region can be restored by either. This demonstrated that these two elements interact in a mutually dependent and similar manner. Furthermore, a DNA fragment that includes the CArG boxes had significant competitive activity for transcription directed by the alpha-cardiac actin promoter in an in vivo competition assay. We conclude that the two sequences around each CArG box may interact with the same class of trans-acting positive factor(s) and that these interactions may mediate muscle-specific expression. Each of the two CArG regions appears to be bound independently by such a positive factor(s), and the regions support high-level transcription in a synergistic manner. The transcriptional activity of this regulatory region is proportional to its distance from a TATA box (at -30 bp) and is strictly orientation dependent relative to the direction of transcription. Therefore this upstream region is not an enhancer but is a tissue-specific regulatory upstream element.
Miwa et al. (Sat,) conducted a other in Gene expression in muscle cells. Promoter region modifications (5' deletions, linker-scanning mutations, insertion-deletion mutations) was evaluated on Transcriptional activity of the human alpha-cardiac actin gene. Two CArG box domains at -140 and -100 bp in the human alpha-cardiac actin gene promoter act synergistically and mutually dependently as tissue-specific regulatory upstream elements for transcription.